Kiswahili is a very important language in Kenya. It is both a national and official language in the republic of Kenya. However, there are concerns that the poor performance in Kiswahili in national examinations is partially attributed to the laxity in the enforcement of the school language policy. The objective of the study was to assess how the motivation, structure and enforcement of the school language policy impacts on the use of Kiswahili within the school setting, The study was conducted in 30 out of 300 public secondary schools found in Bungoma County. The respondents were 360 form three students, 90 teachers of Kiswahili and 30 principals. Stratified, purposive and simple random sampling techniques were used to sample the target groups. The questionnaire, FGD guide and document analysis guide were used to collect data. The data was analyzed using descriptive statistics which included the use of frequencies, percentages and narrations. The study established that the sampled schools had language policy in place although it varied. Some schools had structured language policy while others had unstructured language policy. It was found out that motivation and punishment had an impact on the enforcement of school language policy. In view of the above findings, it was recommended all teachers regardless of the subject they teach should participate in the enforcement of the school language policy. The school administrators should ensure that their respective language policies should be fully enforced in order to meet its intended purpose and the school language policies should be well structured. It is hoped the finding of this study would help MOEST, principals of schools and teachers in formulating school language policy that aim at enhancing students achievements in languages offered in the curriculum.